Process for the manufacture of sodium percarbonate



Patented Aug. 31, 1948 Victor-Wallace Slater, Luton, and William Stanley Wood, .Harpen'den, England, .assignors to lalorte Limited,Luton,-Bedfordshire, Eng-. an l i No Drawing- Ap ca i n uly .1, .4 Se iI 544,460. In Great Britain August 9, 1943 4 Claims- (erase-s2) -1 Thisinvention relates to themanufacture of sodium percarbonate.

Various processeshave been proposed iorthe manufacture of sodiumper-carbonate, for exam- "dium carbonate-in proportionate quantities 'Itwas further foundthat in the present process the use of sodium silicateas a stabiliser is preferable to magnesium sulphate or magnesiumtrisilicate. The sodium silicate results in a better -p1e that describedin United Kingdom specifica- 15 and morestable product with a higheryield. tionNol. 502,319. The composition of the sodium silicate is rela-It is an object of the present invention to protively unimportant andsolutions of sodium sili- V de n improved process for the manufacturecate with ratios of sodium oxide (NazO) tosllica f gu pe ca o atedhav gcertain advan- I (SlOz) varyingirom 1:1to1:3.4 may be used with tagesereinafter referre to. :10 equal satisfaction. The important factor isto With this object in view the presentVin-vention standardise thequantity of S102 added. It is vprovides .a cyclic process for themanufacture of neeessaryto employ a quantity of sodium silicatesodliumdgerc'arbtgnati whereiizldhsdrogerlltpe o q coming'withinaspecified range in order to obtain an so 11m car ona e are a 6 91180118Y the most satisfactory results as regards the efiior alternately insmall quantities to the mother l5 ciency and granular atu e of theproduct, 'It llqy i a p g ous p p tat mbe t has been found convenienttoex ress the quanln e manu ac ure 0 so ulum p e e e tity of sodiumsilicate to be added to the making according to the process of thepresent invention in t s of grams of SlOz per litre of hydrogen thesodium carbonate and hydrogen peroxide-are e xi o molar strength, i. e.340 grams -Preffe1'ab1Y added in the proportion, required 1-1262 perlitre of solution. It has been found that t hg fOIIllUlQ, ZNEEZCQELIHZOQWhile, Inailfltaininga obtain th most satisfactory results the quanbe PG, .g v. :H ,l of gramsto rams-S10- erlireof Omolar of the Sodiumpercarbona-te'formed'andv-enajblgs hydrogen peroxi e. For d ii terentstrengths of h P P be e ei gm l o g l i hydrogen peroxide the amount ofsilicate added @F'X P l nfi e s Q l m .e t is based on the abovequantities. For example, fitttttftit irritation in if g of to e; e 1 l,71 1. s xedatlvv ramsSO.. r f lmo r i m percarbonate isiprecipitated-non?- F ('o lr/ viaveight by volu me; lfyd ge n ge oxide,th n gr f ge sg ig 2 z z gg ggg zhus zr is: use whenusing so% weightbyVolume hydrogenper- -bility of the sodium percarbon ate may bel stillOmdeQthB smcatefdded woulq be grams S102 further reduced by the additionof sodium chlof 1mm hydiPgeI; g i by voume. eraloo 12 oavaia eoxygen g?metal salt sufphbdgiifiodl'um is, therefore, the same in both cases.After the 119 t s 8 O m ess 0 S 5\first'two additionstof hydrogenperoxidatso dium bonate has been found tobe between rm and', 5 in t a drbon m 1 ms per litre of solution over and above that 51 n 1 mppe-n Avga1 th H 0 based on themtio that. no preclpltate of sodium percarbonateis V e o e 2 2 formed;butagelatinous siliceous precipitate sepa2Na2COa3I-I202 arates which is undesirable as it tends to impairthergranular'nature and filtering properties: of

( It is possible toworl; with a larger excess of l sodium carbonate, butthis affects the filt ti the final p eclpltate For this reason theaddispropertvies of the final product! There is also a ,tlon oi the-sodum. silicate may be delayeduntil itendency for the granular nature oftheI prompt the third addition of hydrogen-peioxide, and the todeteriorate as the excess of sodium carbonate {luantlty added In eachaddltlon adJuSted PF iS inc d. Thedeterioratio in granular pa- 'mgly. Ithas also-been found that the addition ski-[lure f the precipitateresults inincreasedqpan, vo i staluhser 1s best. madeat the time of theadditities of mother liquor being retained by the 'pret1n$-0fhydr?genperoxlde and Sodlum L cipit ate and results in indreased ogygenllpssesuandiifl-the simultaneous method ofaddition is during drying with anincrease in the amount adopted; the stabiliser should either be added at,q-f solids other than sodium percarbonate in the gee la mg a the agmlied *final product. irec y Wl e y rogen peroxi e. en yv It was fou ndthat the addition of the usual drogen peroxide solutions of highstrength, e. g. stabilisers was advantageous and that they were 60%weight by volume are used it is recombest added with the hydrogenperoxide and somended' thatthe sodiumsilicatebe added directly tothe-making and not mixed'withthe concen- It was also found that theaddition of sodium metaphosphate favourably affects the *granular natureof the precipitate. The amount of sodium metaphosphate added to themother liquor may be reduced as the cycle proceeds. found that thehydrogen pero-xidemay be added in concentrations up to the highest whichcan be prepared. The process infactlends itself particularly to the useof solutions of hydrogen per- It ,was also oxide of high concentration,e. g. 60%, thus reducing the amount of mother liquor which has to berejected owing i-.ito excess volume. The mother liquor is filtered orclarified beforere-use.

If the additions of hydrogen peroxide and sodium carbonate are alternatethen the basis of the additions should be such that the amount of so-'dium carbonate added at a time should not exceed 20 gms. per litre withthe stoichiome tric quantity of hydrogen peroxide after allowing forexcess sodium carbonate to maintain concentration and the specifiedquantity of stabiliser. This ensures thegranular nature of the product;if more than 20 gms. per litre is added then the granular nature of thepercarbonate deteriorates. As previously stated, it is advantageous tohave 40 gms. of excess sodium carbonate p r litre as a minimum.

The process can be carried out with solutions containing differentconcentrations of sodium chloride, but in order to reduce the losses dueto oxygen decomposition it is best carried out with concentrations offrom 200-280 gms. of sodium chloride per litre. The sodium chloridecontent has an important effect on the yield and stability of the finalproduct. This may be seen from the following figures:

Solution content Results Oxygen yield NaCl Excess NazCO; gg fi f as dampg g percarbonate Grams/litre Grams/litre Percent Percent Similarly, ifthe sodiumchloride content of the solution is increased above themaximum figure given above, the quality of the precipitate againdeteriorates. The salt concentration of the solution may be adjustedeither periodically during the making or at the end of the making, thelatter being particularly convenient for high strength of materials, theloss due to decomposition is reduced to a minimum whilst the processdoes not .filtered by means of a centrifuge. after clarification wasused for preparing another 4 require special cooling and may be carriedout at normal room temperature and even up to about 25 C. whilst theproperties and quality of the sodium percarbonate obtained aresatisfactory in every respect.- Also, the process of the presentinvention allows for a verylarge number of additions to be made due tothe granular quality of the product. It has been found possible to makeas many as 18 additions of 89 lbs. of hydrogen peroxide of 30.4%, weightby volume to a batch of 500 gallons.

In carrying out the present invention according to a preferredembodiment, the requisite quantity of sodium metaphosphate is added tothe clear mother liquor from a previous batch and the temperature isadjusted to not less than 15 C. The first two additions of sodiumcarbonate and hydrogen peroxide may be made without the addition ofsodium silicate. The subsequent additions consist of proportionatequantities of sodium carbonate, and hydrogen peroxide and sodiumsilicate, the latter two being mixed together when using lower strengthsof hydrogen peroxide.

The additions may be made at five minute intervals. Thetime between eachaddition depends upon the amount of hydrogen peroxide and sodiumcarbonate added at each addition. As stated previously the maximumamount of sodium carbonate added should not exceed a quantity equivalentto more than 20 grams NazCOs per litre. For such a quantity it has beenfound that the tim between additions should be five minutes. For smalleradditions it has been found that the time interval may be reduced butshould not be less than two minutes. During the making the temperatureis allowed to rise to 22 C. and maintained at this figure until thefinal addition of salt has been made. The batch is then filtered with orwithout cooling, e. g. to 15 C.

The following examples illustrate how the process of the invention maybe carried into effect:

1. 450 gallons of a solution of the following composition: 250 gms, ofNaCl per litre, 40 gms. of NazCoa per litre, and 2.5 gms. of availableoxygen per litre were run into a vat of 700 gallons capacity fitted withan agitator running at 36 R. P. M. To this solution, the temperature ofwhich was 15 C., was added 7 /2 ozs. of sodium metaphosphate. Over aperiod of one or two minutes there was added 89 lbs. of hydrogenperoxide containing 30.4 gms. of H202 per 100 mls., 0.5 gallon of sodiumsilicate (Na2O.3.2SiO2) solution of Tw., and 56 lbs. of anhydrous sodiumcarbonate.

The batch was allowed to agitate for 3 minutes after which a furtheraddition of 89 lbs. of the aforesaid H202, 0.5 gallon of the aforesaidsodium silicate solution and 56 lbs. of anhydrous sodium carbonate wereadded over a period of 1 to 2 minutes. The batch was allowed to agitatefor 3 minutes and the additions of hydrogen peroxide,

sodium silicate and sodium carbonate continued as above until a total of12 additions had been made. The sodium percarbonate separated as agranular precipitate and there was no sign of decomposition during theprocess. There was a gradual rise in temperature until after the fourthaddition the temperature was 22 C. The batch was maintained. at thistemperature for the remainder of the process. After the completion ofthe 12 additions, 250 lbs. of common salt were added to re-adjust theconcentration of NaCl which had decreased due to dilution during theprocess. The batch was cooled to 15 C. .and The filtrate batch of sodiumpercarbonate in the manner described above, whilst the damp residue ofsodium percarbonate containing 11.3% of available oxygen was driedWithout decomposition to give a fine, granular, free flowing, stablepowder containing 13.3% of available oxygen. The efficiency of therecovery of the oxygen as sodium percarbonate was equal to 96%. Theavailable oxygen present in the solution at the start of the processrepresents the solubility of sodium percarbonate in a solution of sodiumchloride and sodium carbonate of the concentrations given and at thetemperature of the previous filtration.

2. 500 gallons of mother liquor from a previous precipitation were runinto a vat and 9 ozs. of sodium metaphosphate were added. There werethen made, in the same manner as in Example 1,

11 additions of 57 lbs. of hydrogen peroxide 60% weight by volume 11additions of 58 lbs. of soda ash 11 additions of 3 pints of sodiumsilicate solution (1.30 sp. gr.)

After the 11 additions had been made, 154 lbs. of sodium chloride wereadded. After cooling to 15 C. the percarbonate was filtered by means ofa centrifuge and dried. The dried sodium percarbonate containing 13.74%available oxygen with an overall oxygen yield as sodium per-carbonate of97.3

We claim:

1. In a cyclic process for the manufacture of sodium percarbonate byreacting sodium carbonate and hydrogen peroxide to precipitate sodiumpercarbonate, the improvement which consists in adding hydrogen peroxideand sodium carbonate to a mother liquor from a previous precipitationcontaining sodium chloride, sodium carbonate and available oxygen assoluble sodium percarbonate, and so controlling the amounts and rates ofaddition of hydrogen peroxide and sodium carbonate as to maintain thesodium carbonate in solution and the content thereof in the reactionmixture throughout the course of the reaction at between 40 and 60 gms.per liter of solution in excess of the proportion required by theformula ZNazCOaBHzOz.

2. The process according to claim 1 wherein the hydrogen peroxide andsodium carbonate are added to a mother liquor from a previousprecipitation containing, besides sodium carbonate and available oxygenas soluble sodium percarbonate, between 200 and 280 gms. of sodiumchloride per liter.

3. The process according to claim 1 wherein the hydrogen peroxide andsodium carbonate additions to the mother liquor are made alternately inincrements of which the sodium carbonate additions do not exceed 20 gms.per liter of the reaction mixture and the intervals between theincremental additions are so spaced as to insure substantially completereaction of the hydrogen peroxide and sodium carbonate present in themixture before fresh additions are made.

4. In a cyclic process for the manufacture of sodium percarbonate byreacting sodium carbonate and hydrogen peroxide to precipitate sodiumpercarbonate, the improvement which consists in periodically addingsodium carbonate and hydrogen peroxide to a mother liquor from aprevious precipitation containing sodium chloride, sodium carbonate andavailable oxygen as soluble sodium percarbonate and being otherwisesubstantially free from hydrogen peroxide, and so controlling theamounts and rates of addition of hydrogen peroxide and sodium carbonateas to maintain the sodium carbonate in solution and the content thereofin the reaction mixture throughout the course of the reaction at least40 gms. per liter of solution in excess of the proportion required bythe formula 2Na2COs.3H2O2.

VICTOR WALLACE SLATER. WILLIAM STANLEY WOOD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,225,832 Liebknecht May 15, 19171,237,128 Weber Aug. 14, 1917 1,263,258 Liebknecht Apr. 16, 19181,950,320 Muller Mar. 6, 1934 1,986,672 Bergman Jan. 1, 1935 FOREIGNPATENTS Number Country Date 152,366 Great Britain Oct. 21, 1920 502,319Great Britain Mar. 15, 1939 Certificate of Correction Patent No.2,448,058. August 31, 1948.

VICTOR WALLACE SLATER, ET AL.

It is hereby certified that the name of the assignee in the abovenumbered patent was erroneously described and specified as B. La PorteLimited whereas said name should have been described and specified as B.Laporte Limited, as shown by the record of assignments in this Office;and that the said Letters Patent should be read with this correctiontherein that the same may conform to the record of the case in thePatent Oflice.

Signed and sealed this 5th day of April, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

